In science in general, including computer science, "theoretical" doesn't mean fringe or unexplored, it means foundational and abstract. CS theory uses the word "theory" in the same sense as music theory. CS theory deals with well-defined, rigorous analysis of computation in abstract or mathematical terms.
I would have assumed that was a mononomial for just one and two of them are a binomial but apparently polynomial is used instead even for only one or two?
A two-termed polynomial is also called a binomial. "Binomial" and "monomial" are special cases of the more general term "polynomial".